(1) Field of the Invention
The present invention relates to a deep-draw-formed vessel prepared from a laminate of an iron or steel foil and a plastic material. More particularly, the present invention relates to a deep-draw-formed vessel excellent in corrosion resistance, shape-retaining property and easy disposability. Furthermore, the present invention relates to an improvement of the deep-drawability of a laminate comprising an iron or steel foil and a resin film.
(2) Description of the Prior Art
As the packaging material for a vessel or lid, there have been used various single materials such as metals, plastics, paper, glass and ceramics, and composite materials comprising at least two of these single materials. However, in view of the combination of the barrier property to gases such as oxygen, carbon dioxide gas and steam and the mechanical strength, metal materials are most preferred.
In case of a metal can or metal lid, there arises a problem of so-called can pollution because disposal is impossible by incineration. Accordingly, as a packaging material having an easy disposability, a laminate comprising a metal foil and a resin film is widely used in the field of sealed vessels or sealed lids. Almost all of commercially available laminates for vessels or lids comprise an aluminum foil as the substrate. Although an aluminum foil is excellent in appearance characteristics and flexibility, even in the state covered with an organic resin, troubles such as corrosion, i.e., pitting, and peeling of the covering layer are caused by a content containing a salt such as sodium chloride at a high concentration or a content containing an organic acid, and such defects as leakage the content and reduction of the preserving property are brought about.
As the metal foil, there also are known foils composed mainly of iron or steel, such as an iron foil, a steel foil and a tinplate foil. However, use of these foils as the packaging material involves problems to be solved. Namely, rusting is readily caused in iron and steel, and during the preparation of a packaged article or during the storage, rusting is caused and drastic reduction of the appearance characteristics or commercial value often occurs. Furthermore, dissolution of iron or incorporation of rust results in drastic reduction of the property of retaining the flavor of the content.
In a vessel obtained by deep-draw-forming a laminate comprising a steel or iron foil or the like and a resin film, even if the steel or iron foil or the like is covered with the resin film on the inner face side, peeling is readily caused between the resin film layer on the inner face side and the steel or iron foil, and even when peeling is not caused after the forming operation, peeling is caused at the time of retort sterilization or during the subsequent storage, a so-called blister is formed in this peeled portion and corrosion or dissolution of iron is caused from this blister.
Furthermore, since the thickness of an iron foil or steel foil is smaller than the thickness of a steel plate, the iron or steel foil is poor in drawability and formability, and during the draw-forming operation, the foil is wrinkled or broken and it is impossible to form a vessel. This defect becomes conspicuous when an organic resin covering layer having a relatively large thickness is applied to the iron or steel foil so as to improve the corrosion resistance or rust resistance of the foil.